In general daily life, various lighting devices can be seen everywhere, such as fluorescent lamps, street lamps, table lamps, art lamps, and the like. In the above lighting apparatus, a tungsten filament bulb is conventionally used as a light source. In recent years, due to the rapid development of technology, light-emitting diodes (LEDs) have been used as sources of illumination. In addition, in addition to lighting equipment, for general traffic signs, billboards, lights, etc., also use LEDs as a light source. As mentioned above, the use of light-emitting diodes as light-emitting sources has the advantages of power saving and greater brightness, so it has gradually become common in use.
With the development of lighting technology, people are increasingly demanding light sources, especially dimming functions. At present, dimming function has become a must-have function of LED lamps, especially in the North American market. At the same time, with the development of the industry, people no longer only pursue the dimming function, but also require the quality of dimming, that is, high requirements about no stroboscopic lighting, dimming depth, even softness, comfort, etc. A conventional LED constant current drive scheme has a DC/DC converter that converts the varying input current into a constant current output of varying amplitude. Therefore, the conventional LED constant current driving scheme is the mainstream of the current market, and has the advantages of simple circuit, high stability, fast response, no compensation, high efficiency, and can be dimmed using PWM signals, or dimmed by amplitude. However, due to the structure and working principle of the DC/DC converter itself, if the dimming is only performed by the amplitude, the dimming depth is not enough for the occasions requiring high dimming performance, generally only 10%. Up to 20%, not to mention 1% or lower dimming depth, and the lower the dimming depth, the lower the accuracy. If only PWM dimming is used, due to the characteristics of the PWM signal itself, that is, there is a duty cycle, there will inevitably be stroboscopic. In order to reduce the stroboscopic factor, only the frequency of PWM dimming is increased. However, as the dimming frequency increases, the operating frequency of the DC/DC converter must also increase accordingly, thereby ensuring the stability and accuracy of the DC/DC converter. At the same time, the increase of the operating frequency of the DC/DC converter will inevitably lead to the problem of reduced efficiency and EMI degradation.